Interpretive Summary: Carcass traits are the lens through which consumers view the end-product of beef production. Marbling has long been held as an indicator of palatability and serves as a basis for determining the price of beef. Marbling is moderately heritable and thus amenable to genetic improvement. Animals must be harvested to directly measure marbling and progeny testing lengthens the generation interval thereby slowing progress. Thus, there is a need to develop accurate indicators of genetic potential for marbling that can be measured early in its life. This research was conducted to evaluate one such indicator, a panel of molecular genetic markers. The results confirm the usefulness of this panel, while also indicating a need for its continued improvement if it is to negate the need for progeny testing. These results are being used by commercial providers of national and international genetic evaluations of beef cattle, companies that produce marker panels, seedstock producers, and ultimately commercial beef producers as they seek to better meet consumer expectations.

Technical Abstract:
Objectives were to estimate genetic parameters needed to elucidate the relationships of a molecular breeding value for marbling (MBV), intramuscular fat of yearling bulls measured with ultrasound (IMF) and marbling score of harvested steers (MRB), and to assess the utility of MBV and IMF in prediction of breeding value for MRB. Records for MRB (n = 38,296) and IMF (n = 6,594) were from the American Angus Association data base used for national cattle evaluation. There were 1006 records of MBV used in this study. (Co)variance components were estimated with ASREML fitting an animal model with fixed contemporary groups for MRB and IMF similar to those used in national genetic evaluation of Angus. The overall mean was the only fixed effect included in the model for MBV. Heritability estimates for carcass measures were 0.48±0.03, 0.31±0.03, and 0.98±0.05 for MRB, IMF, and MBV, respectively. Genetic correlations of IMF and MBV with MRB were 0.56±0.09 and 0.38±0.10, respectively. The genetic correlation between IMF and MBV was 0.80±0.22. These results indicate the MBV evaluated may yield approximately 20% greater genetic advance when used as an indicator trait for genetic prediction of MRB than IMF. However, neither of these indicators alone provides sufficient information to produce highly accurate prediction of breeding value for the economically relevant trait MRB. Given the goal of highly accurate prediction of EPD for MRB, results of this work point to the need to 1) use progeny testing and 2) increase the genetic correlation between the MBV and MRB.